Waves

Waves

1. Terminology

   • Crests
     • Maximum positive displacement
   • Troughs
     • Maximum negative displacement
   • Wavefront
     • The whole width of a wave crest
   • In Phase
     • If two points on a wave have the same displacement, and have the same velocity at a particular instant in time.
   • Amplitude
     • The maximum particle displacement form the undisturbed state
   • Wavelength
     • The distance between two adjacent points in phase
   • Frequency
     • The number of waves that pass a fixed point per second
   • Period
     • The time it takes for one complete wave to pass a fixed point
   • Propogation
     • Wave movement
   • Wave speed
     • The velocity with which a wave propogates / transfers energy away from the source
   • Medium
     • The material / substance in which the wave propogates

2. General

   • The source of all waves is a vibration.
   • Waves may travel in 1, 2, or 3 dimensions.
   • Waves transfer from one place to another, without the transfer of matter.
   • Wave Types
     • Electromagnetic
       • Propogates as a perpendicular and magnetic field. It does not need particles.
     • Mechanical
       • Requires the movement of particles to propogate
     • Transverse
       • the vibrations are perpendicular to the direction the wave is travelling.
       • Consists of Crests and Troughs
     • Longtitudinal
       • The vibrations are backwards and forwards (in parallel to the direction of propogation)
       • Consists of Compressions and Rarefactions

3. Sound

   • Longitudinal Wave
   • Sound waves can travel in any medium, but travel fastest in solids.
   • Greater Amplitude = Greater Volume
   • Higher Frequency = Higher Pitch
   • Echoes
     • Sound waves reflected back at you
     • To hear one, there needs to be a distinguishable time between the two sounds so that they are distinguishable.
     • Sonar
   • Superposition
     • At the point where two or more waves meet, the displacement of the medium is the sum of the displacements of the individual waves.
     • Constructive Interference
       • Two crests add to make a crest of larger displacement
     • Destructive Interference
       • When a crest meets a trough, they cancel each other out

4. Beats

   • When two periodic waves of slightly different frequency interfere the resultant wave shows instances of large displacement and others of small displacement.
     • The large displacements correspond to a loud sound and the small displacements to a quiet sound leading to a periodic throbbing sound.

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